How Does Power Steering Work

How does power steering work? There are two types of power steering systems: the rack and pinion, which is the most widely used, and the recirculating ball, which has been used from the beginning and is still in use in trucks today.

Rack and Pinion

The rack and pinion consists of two primary parts: the power steering pump and the rack and pinion. The rack and pinion is a metal tube, approximately three inches in diameter and three feet long, installed perpendicular behind the wheels. Inside the tube is a flat piece of metal with large teeth cut into the topside of it. There is a round seal located in the center of the rack sealing either side of the rack. On the driver's side is the steering shaft input and control mechanism. There is a tie rod assembly attached to each side of the rack, which is attached to each spindle.

High-pressure hydraulic fluid from the power steering pump enters the steering mechanism through a hose and another hose returns the fluid to the power steering pump. There are two high-pressure hoses from the steering mechanism going to either side of the center seal. When the steering wheel is turned in either direction, an orifice in the steering mechanism is exposed allowing high pressure hydraulic fluid to pass to one side of the rack which is sealed in the center. This pressure pushes the seal and rack in that direction, giving your power an assist. The pressure is simply directed to one side or the other of the center seal for directional control.

Recirculating Ball

This is the oldest system and still in use. It is a smaller unit attached to the driver's side frame. It consists roughly of a foot long shaft threaded much like a screw in a housing that is angled toward the steering column. It has an input shaft attached to the screw mechanism. The steering column is attached to this shaft by a round, flexible piece of sturdy material called a rag joint. There is a large round nut inside the assembly, which is in the middle of the threaded shaft, called the sector shaft. To the bottom of the sector shaft is attached a pitman arm. This arm is the driving force to turn the wheels. The pitman arm is attached to a drag link, or long rod that runs the width of the undercarriage and is supported on the passenger side by an idler arm. Tie rods are attached to this long arm on either side. These tie rods are further attached to the wheel's spindles.

This system works almost identical to the rack and pinion. High-pressure fluid is passed to the steering mechanism where a separate orifice opens for either a left or right turn. This directs high-pressure fluid to either side of the large center nut on the sector shaft pushing it up or down turning the sector shaft in the process.

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